Dark data refers to information your company collects but never uses—often...

https://domgodwinson38.gumroad.com/p/how-do-i-check-if-dark-data-contains-pii-or-phi

Dark data refers to information your company collects but never uses—often making up 55% of stored files. This unused data takes up space, drives up storage and backup costs, and increases ransomware risk since it’s often unmonitored